154 TIMBERS AND THEIR USES 



and fermentation takes place with the consequent 

 destruction of the Hgnified cell walls. The care- 

 ful forester, when he finds it necessary to cut 

 away part of a tree, covers the wound with a 

 preservative so that decay may be prevented 

 till such time as the natural growth of the tree 

 covers the spot with a new layer of bark. When 

 wounds are left untended decay gradually 

 spreads down the centre of the stem and thence 

 outwards with the result that the centre of the 

 tree rapidly becomes hollow. It is always wise 

 to carefully examine the wood below an old 

 wound to discover the extent of decay, for an 

 exterior inspection will not reveal the fact. In 

 certain cases, and for a limited number of pur- 

 poses, partially decayed wood is in request, but, 

 speaking generally, all timber which is " foxy " 

 or shows any signs of decay is materially reduced 

 in value. 



Another defect, and fortunately only a local 

 one, may arise from injury to the bark. As we 

 have already explained, in the event of injury 

 the tree forms new layers of tissue to cover the 

 wound. Should the injury not be deep seated 

 little harm may result beyond a slight scar on 

 the bark. If, however, the damage extend 

 to the cambium, the tissue from which new 

 wood is formed, although heahng growth may 

 take place, the new wood may fail to adhere 



